非对称氧掺杂对石墨烯/二硒化钼异质结肖特基势垒的调控

在纳米逻辑器件中,制造低的肖特基势垒仍然是一个巨大的挑战.本文采用密度泛函理论研究了非对称氧掺杂对石墨烯/二硒化钼异质结的结构稳定性和电学性质的影响.结果表明石墨烯与二硒化钼形成了稳定的范德瓦耳斯异质结,同时保留了各自的电学特性,并且形成了0.558 eV的n型肖特基势垒.此外,能带和态密度数据表明非对称氧掺杂可以调控石墨烯/二硒化钼异质结的肖特基接触类型和势垒高度.当氧掺杂在界面内和界面外时,随着掺杂浓度的增大,肖特基势垒高度都逐渐降低.特别地,当氧掺杂在界面外时, n型肖特基势垒高度可以降低到0.112 eV,提高了电子的注入效率.当氧掺杂在界面内时, n型肖特基接触转变为欧姆接触.平面平均电荷密度差分显示随着掺杂浓度的增大,界面电荷转移数量逐渐增多,导致费米能级向二硒化钼导带底移动,证实了随着氧掺杂浓度增大肖特基势垒逐渐降低,并由n型肖特基向欧姆接触的转变.研究结果将对基于石墨烯的范德瓦耳斯异质结肖特基势垒调控提供理论指导.     

平面异质结有机-无机杂化钙钛矿太阳电池研究进展

高效低成本太阳电池的研发是太阳能光伏技术大规模推广应用的关键. 近年来兴起的有机- 无机杂化钙钛矿(以下简称钙钛矿)太阳电池因具有光电能量转换效率高、制备工艺简单等优点, 引起了学术界和产业界的广泛关注, 具有广阔的发展前景. 其中平面异质结钙钛矿太阳电池因具有结构简单, 可低温制备等诸多优点, 成为目前研究的一个重要方向. 平面异质结钙钛矿太阳电池分为n-i-p型和p-i-n型两种结构. 其中钙钛矿分别与电子传输层和空穴传输层形成两个界面, 在这两个界面上实现电子和空穴的快速分离. 电子传输层和空穴传输层分别为电子和空穴提供了独立的输运通道. 平面异质结结构有利于钙钛矿太阳电池中电子和空穴的分离、传输和收集. 此外, 该结构不需要高温烧结的多孔结构氧化物骨架, 扩大了电子和空穴传输材料的选择范围. 可以根据钙钛矿材料的能带分布及载流子传输特性, 来选择能级和载流子传输速率更为匹配的传输材料. 本文对钙钛矿的材料特性, 平面异质结结构的由来及发展进行了简要的概述. 其中重点介绍了平面异质结钙钛矿太阳电池的结构特征、工作机理、钙钛矿/电荷传输层的界面特性, 以及电池性能的优化, 包括钙钛矿薄膜制备、空穴和电子传输层的优化等. 最后对钙钛矿电池的发展前景及存在问题进行了阐述, 为今后高效、稳定钙钛矿太阳电池的研究提供参考.     

可实现宽频带光波非对称传输的自准直效应光子晶体异质结构

利用光子晶体的自准直效应和能带特性,设计了一种能实现宽频带光波非对称传输的二维光子晶体异质结构.该结构实现宽频带、高正向透射、非偏振选择的非对称传输.横电(transverse electric, TE)偏振光非对称传输波长带宽可达532 nm,在光通信波长1550 nm处正向透射率和透射对比度分别可达0.693和0.946;横磁(transverse magnetic, TM)偏振光非对称传输波长带宽为128 nm,在光通信波长1550 nm处正向透射率和透射对比度分别可达0.513和0.972;通过进一步优化异质结界面,在TE偏振光下非对称传输波长带宽可达562 nm.     

基于二维六方氮化硼材料的光子晶体非对称传输异质结构设计

二维六方氮化硼(hexagonal boron nitride,hBN)材料在产生光学稳定的超亮量子单光子光源领域有着潜在应用,有望用于量子计算和信息处理平台,已成为研究热点.而光学非对称传输设备是集成量子计算芯片中的关键器件之一.本文从理论上提出了一种基于hBN材料光子晶体异质结构的纳米光子学非对称光传输器件.运用平...     

掺杂两种荧光染料的有机红光电致发光器件

制作了掺杂rubrene和4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9,enyl)-4H-pyran(DCJTB)两种荧光染料的红光有机电致发光器件。N,N’-diphenyl-N,N’-bis(1-naphthyl)-(1,1’-biphenyl)-4,4’-diamine(NPB)和掺杂的Tri-(8-hydroxyquinoline)aluminum(Alq3)分别作为空穴和电子传输层。我们发现掺rubrene和DCJTB的器件性能与只掺DCJTB的器件性能相比有所提高。器件性能的改善是因为掺入的rubrene能够促进从Alq3到DCJTB的能量转移。根据荧光衰减曲线,计算出从Alq3到DCJTB、从Alq3到rubrene以及从rubrene到DCJTB的能量转移速率分别为1.04×109,3.89×109,2.79×109s-1。可以看出能量通过rubrene从Alq3到DCJTB的转移速率是能量直接从Alq3到DCJTB的2.7倍。     

基于隧穿氧化物钝化接触的高效晶体硅太阳电池的研究现状与展望

在当今的光伏市场,晶体硅电池占据超过九成的份额,并且被认为在未来将依旧占据主导地位.在高效晶硅电池中,隧穿氧化物钝化接触太阳电池(tunnel oxide passivated contact solar cell,TOPCon)因其优异的表面钝化效果以及与传统产线兼容性好的优势而受到持续关注.该电池最显著的特征是其高...     

Siδ掺杂AlxGa1—xAs／GaAs异质结二维电子气的SdH振荡研究

使用分子束外延方法生长了一种新的基于Ｓｉδ掺杂的ＡｌｘＧａ１－ｘＡｓ／ＧａＡｓ异质结，测量了０．３－３０Ｋ低温下异质结处二维电子气的横向磁阻、迁移率和Ｈａｌｌ电阻，磁阻的Ｓｈｕｂｎｉｋｏｖ－ｄｅ Ｈａｓｓ（ＳｄＨ）振荡非常明显。对振荡曲线作快速Ｆｏｕｒｉｅｒ变换分析，获得了二维电子气中每一子能带上占据的电子数密度和有效质量（ｍ＾＊０／ｍ０＝０．０７３，ｍ＾＊１／ｍ０＝０．０６８）。随温度降低，子带     

稀土掺杂CdTe太阳电池背接触层ZnTe的第一性原理研究

结合CdS/CdTe太阳电池背接触层的制备要求考虑, 利用基于密度泛函理论平面波超软赝势方法和广义梯度近似, 计算了未掺杂ZnTe、稀土Y、Gd掺杂ZnTe的能带和电子态密度, 得到了不同体系下系统总能和晶格常数. 研究表明, 稀土Y和Gd掺杂后ZnTe结构的稳定性均提高, 掺杂Y使ZnTe与CdTe的晶格匹配更好. 计算表明, 掺杂可使载流子发生简并, 掺Y比掺Gd电子有效质量小, 掺Y与掺Gd的载流子浓度数量级相同. 根据计算结果分析了稀土掺杂对ZnTe背接触层的影响. 关键词： ZnTe 稀土掺杂 第一性原理 太阳电池背接触层     

新型碳材料在钙钛矿太阳电池中的应用研究进展

新型碳材料如石墨烯及其氧化物、碳纳米管、富勒烯及石墨炔等因其优异的热学、力学、电学、光学性能成为了钙钛矿太阳电池研究的又一亮点. 本文总结了新型碳材料在钙钛矿太阳电池对电极、电子传输材料及空穴传输材料中的研究进展, 新型碳材料的引入有效地提高了钙钛矿电池的性能, 为下一步新型碳材料的应用开发以及钙钛矿电池器件的研究提供了新的思路.     

非对称HALO掺杂栅交叠轻掺杂漏围栅MOSFET的解析模型

为抑制短沟道效应和热载流子效应, 提出了一种非对称HALO掺杂栅交叠轻掺杂漏围栅MOSFET新结构. 通过在圆柱坐标系中精确求解三段连续的泊松方程, 推导出新结构的沟道静电势、阈值电压以及亚阈值电流的解析模型. 结果表明, 新结构可有效抑制短沟道效应和热载流子效应, 并具有较小的关态电流. 此外, 分析还表明栅交叠区的掺杂浓度对器件的亚阈值电流几乎没有影响, 而栅电极功函数对亚阈值电流的影响较大. 解析模型结果和三维数值仿真工具ISE所得结果高度符合.     

钙钛矿/晶硅叠层太阳能电池的研究进展

有机—无机杂化钙钛矿电池因其禁带宽度可调、光吸收系数高、光电转化效率高、制备成本低等优点而被用于硅基叠层太阳能电池中,使得太阳能电池的转换效率提高,生产成本降低,应用范围也更为广泛。文章介绍了钙钛矿吸收材料和钙钛矿/晶硅叠层电池的工作原理,对钙钛矿/晶硅叠层电池的类别、影响其性能的主要因素进行了归纳综述,对钙钛矿/晶硅叠层电池未来发展进行了展望。     

Amorphous/crystalline silicon heterojunction solar cells with black silicon texture

Excellent passivation of black silicon surfaces by thin amorphous silicon layers deposited with plasma enhanced chemical vapor deposition is demonstrated. Minority charge carrier lifetimes of 1.3 milliseconds, enabling an implied open‐circuit voltage of 714 mV, were achieved. The influence of amorphous silicon parasitic epitaxial growth and thickness, as well as of the texture depth is investigated. Furthermore, quantum efficiency gains for wavelengths above 600 nm, as compared to random textured solar cells, are demonstrated in 17.2% efficient amorphous–crystalline silicon heterojunction solar cells with black silicon texture. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Low‐temperature atomic layer deposition of MoOx for silicon heterojunction solar cells

The preparation of high‐quality molybdenum oxide (MoO_x) is demonstrated by plasma‐enhanced atomic layer deposition (ALD) at substrate temperatures down to 50 °C. The films are amorphous, slightly substoichiometric with respect to MoO₃, and free of other elements apart from hydrogen (&11 at%). The films have a high transparency in the visible region and their compatibility with a‐Si:H passivation schemes is demonstrated. It is discussed that these aspects, in conjunction with the low processing temperature and the ability to deposit very thin conformal films, make this ALD process promising for the future application of MoO_x in hole‐selective contacts for silicon heterojunction solar cells. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Dopant‐free back contact silicon heterojunction solar cells employing transition metal oxide emitters

The present study investigates the electrical properties of transition metal oxide (TMO) emitters in dopant‐free n‐Si back contact solar cells by comparing the properties of solar cells employing three TMOs (WO_x, MoO_x and V₂O_x) with varying electrical properties acting as p‐type contacts. The TMOs are found to induce large band bending in n‐Si, which reduces the injection level dependent interfacial recombination speed S_eff and contact resistivity ρ_c. Among the TMO/n‐Si contacts considered, the V₂O_x/n‐Si contact achieves the lowest S_eff of 138 cm/s and ρ_c of 0.034 Ω cm², providing the significant advantages over heavily doped a‐Si:H(p)/n‐Si contacts. The best device performance was achieved by the V₂O_x/n‐Si solar cell, demonstrating an efficiency of 16.59% and an open‐circuit voltage of 610 mV relative to solar cells based on MoO_x/n‐Si (15.09%, 594 mV) and WO_x/n‐Si (12.44%, 539 mV). Furthermore, the present work is the first to employ WO_x, V₂O_x and Cs₂CO₃ in back contact solar cells. The fabrication process employed offers great potential for the mass production of back contact solar cells owing to simple, metal mask patterning with high alignment quality and dopant‐free steps conducted at a lower temperature.     

光管理在晶体硅电池中的应用

光管理是提高晶体硅太阳能电池光吸收和短路电流（Jsc）进而提高转换效率的重要因素之一。本文回顾了最常见的光管理方式,包括表面抗反射、散射以及陷光等。为了降低晶体硅电池的表面反射损失,开发了多种表面抗反射结构。例如,仿生蛾眼结构利用渐变折射率实现了宽光谱低反射率,其表面反射率可达1％以下。随着晶体硅电池衬底减薄,光管理要求更加严格,除了在更宽波长范围内达到超低反射率外,还需要在更高的入射角范围内实现低反射率。此外,利用前表面散射以及背表面陷光结构提高红外光的吸收光程对于晶体硅电池特别是薄衬底晶体硅电池的有效光吸收具有重要意义。     

High-temperature processing of crystalline silicon thin-film solar cells

The crystalline silicon thin-film solar cell combines, in principle, the advantages of crystalline silicon wafer-based solar cells and of thin-film solar cell technologies. Its efficiency potential is the highest of all thin-film cells. In the “high-temperature approach” thin silicon layers are deposited on substrates that withstand processing temperatures higher than 1000 °C. The basic features of the high-temperature crystalline silicon thin-film cell technology are described and some important results are discussed. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Application of crystalline silicon surface oxidation to silicon heterojunction solar cells

We study the effect of ultra-thin oxide (SiO_x) layers inserted at the interfaces of silicon heterojunction (SHJ) solar cells on their open-circuit voltage (V_OC). The SiO_x layers can be easily formed by dipping c-Si into oxidant such as hydrogen peroxide (H₂O₂) and nitric acid (HNO₃). We confirm the prevention of the undesirable epitaxial growth of Si layers during the deposition of a-Si films by the insertion of the ultra-thin SiO_x layers. The formation of the SiO_x layers by H₂O₂ leads to better effective minority carrier lifetime (τ_eff) and V_OC than the case of using HNO₃. c-Si with the ultra-thin SiO_x layers formed by H₂O₂ dipping, prior to deposition of a-Si passivation layers, can have high implied V_OC of up to ∼0.714 V.     

Photographic diagnosis of crystalline silicon solar cells utilizing electroluminescence

The photographic surveying of electroluminescence (EL) under forward bias was proved to be a powerful diagnostic tool for investigating not only the material properties but also process induced deficiencies visually in silicon (Si) solar cells. Under forward bias condition, solar cells emit infrared light (wavelength around 1000 to 1200 nm) whose intensity reflects the number of minority carriers in base layers. Thus, all the causes that affect the carrier density can be detected, i.e., the minority carrier diffusion length (or in other words, lifetime), recombination velocity at surfaces and interfaces, etc. (intrinsic material properties), and wafer breakage and electrode breakdown, etc. (extrinsic defects). The EL intensity distribution can be captured by Si CCD camera in less than 1 s, and the detection area simply depends upon the optical lens system suitable to the wide range of 1 cm–1.5 m. This fast and precise technique is superior to the conventional scanning method such as the laser beam induced current (LBIC) method. The EL images are displayed as grayscale, which leads to the difficulty of distinguishing the sorts of those deficient areas. Since the intrinsic deficiency is more sensitive to temperature than the extrinsic deficiency, the change in solar cell temperature can offer the difference in EL intensity contrasts. These effects upon the measurement temperature can be applied to categorize the types of deficiency in the crystalline Si solar cell.     

Absorption enhancement of ultrathin crystalline silicon solar cells with frequency upconversion nanosphere arrays

A design of ultrathin crystalline silicon solar cells patterned with α-NaEr_(0.2)Y_(0.8)F_4 upconversion nanosphere(NSs) arrays on the surface was proposed. The light trapping performance ofα-NaEr_(0.2)Y_(0.8)F_4 NSs with different ratios of sphere diameter to sphere pitch was systematically studied by COMSOL Multiphysics. The influence of different NS diameters and ratio to the average optical absorption of ultrathin crystalline silicon solar cell was calculated, as well as the short circuit current densities. The results show that the average optical absorption of solar cells with 2.33 μm silicon covered by α-NaEr_(0.2)Y_(0.8)F_4 NSs of 100 nm in diameter and 5.2 in ratio has improved by 8.5% compared to planar silicon solar cells with the same thickness of silicon. The light trapping performance of different thicknesses of silicon solar cells with the optimized configuration of NSs was also discussed. The results indicate that our structure enhances the light absorption. The presented model will be the basis for further simulations concerning frequency upconversion of α-NaEr_(0.2)Y_(0.8)F_4 materials.